1. Field of the Invention
This invention relates to the operation, monitoring and control of a communications system. It is of particular relevance to the operation of telecommunications networks, but is not limited to such systems.
2. Related Art
In this specification the term `functional element` is used to define an element of a communications system which performs some function, e.g. a switching or monitoring function, to the system itself, as distinct from an `application process element` which controls a number of "Functional elements" to achieve a high level function, usually requiring concerted action from several functional elements. This high-level function may be a network application such as a handover process in a mobile radio system.
In a telecommunications network the functional elements of the system are widely distributed. For example, switching functionality is required at nodes throughout the system. However, in conventional telecommunications networks application process control is concentrated, requiring a large signalling load to be carried over the telecommunications network. Despite the distributed nature of the system all elements of the network which interact must have compatible signalling formats. This is a particular problem in a cellular radio network, where mobile units made by a number of different manufacturers can turn up anywhere in the system and have to interact consistently with whichever fixed part of the network they happen to have established communication with. In such a network it is difficult to arrange for enhancement or improvements, because of the need for all signalling formats to remain compatible. Further problems arise in known systems because of the need for measurements of network conditions e.g. link performance to be made, and the results transmitted to a control centre, either continuously or discontinuously depending on the nature of the measurements to be made and the purpose for which they are required. This places an additional signalling overhead on the network. Many measurements are often only required in specific operating circumstances. It is therefore wasteful of signalling capacity for all possible data to be transmitted when much of it is redundant. The limited signalling capacity and the number of different measurements to be made also reduce the resolution of the measurement and/or the sampling rate that can be supported.
A further limitation on capacity in conventional systems is caused by limited routing capabilities. Particularly in a case where a call requiring very high bandwidth or data rate is required, there may be no single route available through the network allowing such capacity. This may be the case even if it is possible to re-route calls in progress without interruption in order to provide greater capacity on a particular link. In these circumstances, a call requiring a higher bandwidth would either fail or cause another lower priority call already in progress to fail, although the system as a whole does have sufficient capacity. Existing telecommunication systems normally permit single links from point to point only. If the link is unreliable, error checking processes may be employed but these require additional data in order to perform the error checking. It is known for mobile units to monitor more than one base station simultaneously, in order to identify the one with the best quality signal. However, in a conventional switched network, because the switching and control of the call are indivisible, the call is handled over a single route only.
Another example of concentration of control is the provision of "conference" facilities in a telecommunications network. In conference bridging, the bridging is set up under the control of a user who sets up a request for bridging to allow more than two users to communicate together simultaneously. This requires an existing link to be bridged to a new one to allow the third caller to communicate with the other two.
In prior art systems, such as that shown in FIG. 10, bridging is only possible in major switching centres 40 and these bridges are of fixed capacity. FIG. 10 shows three terminal units 38a, 38b, 38c arranged to form a `conference call` with each other. Units 38a, 38b are both connected to node 37 but this has no bridging capability. Node 37 and unit 38c are both connected to major switch 40 which has a bridging capability. This means that although units 38a, 38bare both in communication with user 38c through the same node 37 and require a bridge to be made between them, each unit 38a, 38b must be provided with its own bearer 39a, 39b all the way to the mobile switching centre 40. If the bridging could take place at the base station 37, one of the bearers 39a, 39b would be released for other purposes. Referring to FIG. 11, at a switching centre 32 where a bridge is to take place, control processes ensure that each message a,b,c coming into the switching centre 32 is passed from one caller A, B or C on to all other callers.